New syntax introduced: Font, loadFont, textFont, textAlign, text, String, char, textLeading

Loading a font, writing text to the display window

If you want to write text to the screen, Processing has many fonts to choose from. You can pick one by choosing “Create Font” from the Tools drop-down menu. Then in your program, you declare the font variable, load the font, and use the text() function to write text to the screen using the font you created.

Note: Even though Processing itself is platform independent, different operating systems have different fonts. I am a Mac user. If you are a PC user, you might not have the exact fonts I demo in my examples below, but the point is that there are lots to choose from and the way you work them into a program is the same.

Example 5.0

Here is an example of a short program I wrote at the end of the 2011 baseball season using text():

Display output from the code in Example 5.0.

E. Richardson

Here's a screencast walk-through of the program above [2]. (and a captioned version [3].) In the program in Example 5.0, I created the font called “Futura-CondensedExtraBold-36.vlw” by choosing it with the Create Font tool. I have to declare the variable of type PFont at the beginning before the setup() block. Inside the setup() block, I load the font. The function text(data,x,y) in the draw() block takes three arguments: data, which is the thing it will write, and x, and y, which are the coordinates that tell it where to write the data. If you want the text to be colored something other than black, specify the color with fill(). It is a little counterintuitive to some folks that fill(), not stroke(), is how this is accomplished, but that's the way it is. Roll with it. Note that in my program, the sentence, “Cards win!” is enclosed in double quotes because it is a String. The text() function doesn’t need to take String data, it can also be a char, int, or float. You can also have more than one font per program.

Example 5.1

Here’s an example with multiple fonts.

Example source code and output window with pink background and different fonts

E. Richardson

syntax introduced: +=

It’s a little more fun to do something with the text you draw to the screen instead of having it just sit there. Since Processing draws text as an image, you can treat a word just like any other shape.

Example 5.3

Here’s an example in which a word follows the mouse around on the screen (code modified from Reas and Fry, 2007).

Screenshot of output of program above. The word "follow" trails the mouse around the screen

E. Richardson adapted from Reas & Fry

Example 5.4

Here’s an example of a word changing color frame by frame:

Screenshot of program above in which text color changes as the program runs.

E. Richardson

The program in Example 5.4 makes use of the new piece of syntax += which is a compact way to combine addition with assignment. Let's say you have two values: x and y. In Processing,x += y is the same as x = x + y. You are adding the value of y to x and reassigning x the new resulting value all in one step.

Example 5.5

Here’s an example of words that move across the screen

Screenshot of program in Example 5.5 above

E. Richardson

The program in Example 5.5 (screencast walk-through here [4]) (and a captioned version [5]) is meant to demonstrate visually my interpretation of how the last month of the 2011 major league baseball season went for the St Louis Cardinals and the Atlanta Braves. With about a month to go, the Braves had a huge lead in terms of the number of games they had won and seemed to be certain to get into the playoffs. However, they collapsed and lost most of their games over the last month of the season while the Cardinals won so many games that they finished with a better record -- by just one game -- and they got into the playoffs instead. So in the program above, both teams are moving in the same direction, which is kind of like a proxy for time passing. The Cardinals are moving faster because they are catching up, and at the end when both words stop moving, you see that the Cardinals are just a little bit ahead. I added a black vertical line to draw your attention to that fact.

This is an example of a visual representation of an idea or a time-dependent process, which is something that this programming language is good at doing. My guess is that you can be more creative than I am. See if you can come up with moving, changing, or interactive words that represent some kind of idea or process and illustrate it with your program!

New syntax introduced: translate(), pushMatrix(), popMatrix()

You know that the default coordinate system has (0,0) in the upper left corner and increases to the right and downwards. You can change this system by calling the function translate(). The translate() function takes two arguments: the number of pixels added to x and the number of pixels added to y. All shapes drawn after translate() will adhere to the new coordinate structure.

The tricky thing to remember about translation is that you aren't really moving the shapes you draw. Instead you are moving the entire coordinate system relative to the display window. Consider the hand-drawn sketch below in which there is a heart whose top cusp is at (3,2), shown by the black dot.

Red heart on graph paper

E. Richardson

Now if I translate the coordinate system 2 over and 1 down, the display window stays where it is and the heart stays where it is relative to the coordinate mesh, but the coordinate mesh itself has been shifted. So in pseudo-code this would be like:

Heart translated two units to the right and one unit down.

E. Richardson

Translations are cumulative, so the third panel can be achieved either by translating (-5,1) from the second panel, or by translating (-3,2) directly from the first panel. If we had really drawn the third version in Processing, you'd only see the right half of the heart because the other side is out of the display window. Philosophers can tell us whether it exists or not, but in any case we can't see it.

So in pseudo-code this would be:

Or it could have been

Note how I'm always drawing the heart itself with the same coordinates it had in the first place.

Another translation. Either (-5,1) from the second position, or (-3,2) from the original position.

E. Richardson

Example 5.6

Here is an example in an actual program. Notice in this program that rectangle is always specified by the same coordinates. You can see how translation is cumulative and can be negative, too.

Example of cumulative and negative translation

E. Richardson

To change the coordinate system temporarily and then have it go back to the way it was before you made a transformation without having to manually make a negative translation, use pushMatrix() and popMatrix(). These functions always have to be used together. The way it works is that you stick in a pushMatrix() before you write the transformation and then you stick in a popMatrix() just before you want to revert back. The coordinate system will revert back to the way it was before pushMatrix().

Example 5.7

Demonstration of pushMatrix() and popMatrix().

E. Richardson

Note how in the code in Example 5.7 the circle draws in the center of the screen because the for loop was enclosed by a pushMatrix() popMatrix() pair, meaning that all those accumulated translations didn’t affect the circle.

Syntax Introduced: scale()

You can use the function scale() to zoom the coordinate system. It can can take either one argument, or else two arguments if you want to zoom the x and y coordinates differently. In the example below, pay attention to the fact that it's the coordinates that are being stretched, not the shapes. In effect, this means that the position of the shape will change as well as its size.

Example 5.8

Output of Example 5.8. Circles plotted with some scaling changes.

E. Richardson

In the program in Example 5.8, when the coordinate system got stretched, the strokeWeight got thicker, too. The strokeWeight is also affected by scale(). If you don’t want this to happen, you can get around it by dividing the strokeWeight by the scale factor, like this:

Example 5.9

Demonstration of scale() with the strokeWeight fixed.

E. Richardson

Syntax introduced: rotate(), PI, ++, --

You can rotate the coordinate system with the rotate() function. The rotate() function takes one argument, which is an angle in radians. (360 degrees = 2pi radians, so if you don’t like thinking in radians you can specify degrees and then multiply by pi/180 to convert to radians). The rotate() function will by default rotate clockwise around the origin of the coordinate system, so if you want the rotation to occur around a different point, you have to use translate() first to move the origin.

Let's start with the hand-drawn heart from the discussion of translation. Its top cusp is at (3,2).

Heart on graph paper whose upper cusp is at (3,2).

E. Richardson

Now let's rotate by 45 degrees and then draw the heart. In pseudo-code, this would be

Here's what that looks like:

Heart after rotating the coordinate system clockwise by 45 degrees.

E. Richardson

But what if you wanted to rotate the heart itself? The key is to remember that all rotations occur around (0,0). So to make a shape rotate around its own center of gravity, you basically have to draw the shape so that its center is at (0,0). Then you can do whatever rotation you want and it will appear that the shape rotates around itself. But you probably don't want to draw the shape up in the top corner where you can't see most of it! So you translate the coordinate system, thereby putting the origin in the place on the display window that you want, then draw the shape there.

In pseudo-code:

Heart appears to have rotated about the upper cusp because the coordinate system was translated first, then rotated.

E. Richardson

Example 5.10

Here’s an example program that uses translate() and rotate().

Output of Example 5.10. An orange line, then the same line rotated 60 degrees about the point (100,100).

E. Richardson

A screencast explanation of how translate and rotate work in Example [6]5.10, above (and a captioned version [7]).

Do them all! Order matters!

Combining skills!

Example 5.11

Here’s an example of a shape I made with translate and rotate. I turned it into a function and I’m having it move across the screen.

Screenshot of sunrise/sunset program. This program combines a lot of skills learned previously: writing a function, motion, if tests. Also it demonstrates new skills: translate, rotate, pushMatrix, popMatrix.

E. Richardson

A screencast explanation of the sunrise/sunset program [8] (captioned version here [9]). This screencast also provides an introduction to the syntax "++" and "--", which haven't come up before. ++ means increment by 1 and -- means decrement by one. If you write x++ it is equivalent to writing x = x + 1. Similarly, x-- is the same as x = x - 1.